Abubakar Shariff was 'sprayed with bullets' outside a court in Mombasa, Kenya, where he had been attending a hearing

An al-Qaeda leader who is believed to have recruited White Widow Samantha Lewthwaite has been killed in a drive by shooting.

Police said that Abubakar Shariff, also known as Makaburi, was shot dead as he left a court compound 10 miles from Mombasa, Kenya, on Tuesday.

He was waiting outside a court with another man when they were sprayed with bullets from a vehicle that pulled up nearby.

Makaburi was accused by the UN Security Council and U.S. of supporting Somali militant group al Shabaab.

"Our brother Abubakar Shariff Makaburi has left us. He is dead," a preacher at a mosque in Kisauni, a Muslim-dominated area near Mombasa, said through a loudspeaker. "May his soul rest in peace. He has died a brave death."

A witness said Makaburi's had bullet wounds to the body and head. Dozens of Makaburi's supporters gathered nearby demanding police hand over the corpse. Police fired in the air to disperse the crowd.

Makaburi's death could stir fresh unrest in the coastal area where most of Kenya's Muslims live.

Muslim youths clashed with police for three days in February after a man was killed during a police raid on a mosque used by firebrand preachers.

Kenyan police have dismissed Islamist charges that they are to blame for extra-judicial killings. Two other leading Islamists have been killed in the past two years.

Kenya is trying to break up militant recruitment networks among its Muslim community in an effort to end attacks by Somali Islamist militants and sympathisers bent on punishing it for sending troops to Somalia to fight al Shabaab rebels.

He has been linked to Samantha Lewthwaite, 29, the world's most wanted woman, and is believed to be behind the recruitment of more than 100 Britons to al Shabaab.

His death sparked fears of unrest as Kenyan Muslim rights groups threatened to stage street protests unless the government told them who killed Makaburi by Saturday.

Mombasa-based Muslims for Human Rights (Muhuri) and Haki Africa have in the past accused Kenya's Anti-Terror Police Unit of carrying out extra-judicial killings of well-known Muslims, a charge the police have always strongly denied.

Makaburi had told journalists he expected to be assassinated by the police. Makaburi's close ally and friend, preacher Aboud Rogo, was killed in a drive-by shooting in 2012.

"Whichever way we look at it, the government is culpable for either killing Makaburi or for failing to prevent his killing," said Hussein Khalid, director of Haki Africa, a rights group.

Interior Minister Ole Lenku denied government involvement in Makaburi's death and said an investigation had been launched.

"We are certain those criminals will be brought to book and dealt according to law," Lenku said.

Mombasa was calm but tense on Wednesday. Many businesses shut in the city's flashpoint area of Majengo. Trucks full of armed police patrolled palm-lined streets and surrounding areas.

When Rogo was shot dead in 2012, the killing caused several days of riots. The same happened when Rogo's protege was killed in almost identical circumstances in October 2013.

Muslim youths also clashed with police for three days in February after a man was killed during a police raid on a mosque used by firebrand preachers in the Majengo area.

Khalid, flanked by Muhuri members, said the government had three days to "unravel the mystery" of Makaburi's death.

"Failure to (do so means) we shall go to the streets in protest as allowed under our constitution," he added.

The east African country, the region's largest economy, is still reeling from an al Shabaab attack on a shopping mall in Nairobi in September in which at least 67 people were killed.

Security sources say Makaburi had become a leading member of al-Hijra, a Kenyan affiliate of Somalia's al Shabaab.

Muslims accuse Kenya of using heavy-handed tactics to try to dismantle Islamist networks, stirring anger in the Muslim population along the coast who say they are being harassed.

"These kind of killings are not helping. They are only fanning hatred and resistance. Government should find ways of stopping the reckless killings," said Sheikh Mohammad Dor, chair of the Council of Imams and Preachers of Kenya.